The quality of an image prepared from color reversal materials or color negative materials can be adversely affected if the bromide content of the developer is too high. Such materials contain bromide ion, and a quantity of the bromide ion is released into the developer during processing. Hence, the bromide ion content of the developer would tend to increase during use if the developer was not replenished.
Bromide ion has an effect on the rate of development; i.e., as the bromide ion concentration increases, the time for proper development also increases. As can be seen (for example by the description of the E-6 process hereinbelow) standard process conditions specify a set time for development. Hence, in order to have an appropriate amount of development take place in the time allotted, the bromide ion content should be fairly closely controlled.
It is neither economically or environmentally sound to discard photoprocessing solutions after each use. Hence, in most photoprocessing, the formulations are used over and over again, so long as good results are achieved. It is standard practice to add fresh chemicals to seasoned photoprocessing solutions to replace chemicals that are used up during processing steps, or otherwise adjust for changes in content that occur.
Since bromide ion is an important parameter to be controlled, it is highly desirable that its content be readily determined. In sophisticated installations, bromide ion is readily determined using a silver titration and a silver electrode--reference electrode pair. However, that technique is not readily adaptable to use by many ordinary photoprocessors, since such processors generally lack the chemical sophistication and equipment needed to conduct such an analysis.
A titrimetric method using an adsorption indicator is much more adaptable to general use than a method comprising an electrometric end point determination. Silver cation titration of bromide anion in the presence of an adsorption indicator, has been known for a long time; see the references cited below. The heart of such a process is the use of the indicator, which changes color when the titration end point is reached. Adsorption indicators are well known in the art.
The use of 3',3",5',5"-tetraiodophenolsulfonephthalein (TIPS) has been suggested as an indicator for titration of bromide with silver ion. Because of its readily distinguishable color change at the titration end point, its use is preferred in some methods for conducting this invention. However, its use is not a critical feature of the invention.
To determine the bromide ion content in a developer, it is common practice to first neutralize the developer with sulfuric acid in order to deactivate the developing agent(s) present, and prevent unwanted reaction of the developing agents with the silver titrant.
However, sulfuric acid cannot be readily adapted to a method using TIPS or other similar adsorption indicators. For such indicators to work correctly, the acid content of the solution to be titrated must be carefully controlled. In view of the high acidity of sulfuric acid, acidity control is difficult, especially at an installation which lacks the requisite chemical sophistication. Acetic acid is a weaker acid, but its use is not desired because its vapors are irritating.
Furthermore, sulfuric acid and acetic acid are both liquids. Hence, use of these acids in test kits are not preferred, since powdered reagents are preferred, when possible, for inclusion in a test kit to be used by comparatively non-skilled personnel, or to be used by sophisticated personnel who seek to gain the benefits and convenience of a test kit.
Thus, an object of unknown is to provide a titrimetric method for bromide ion content, which comprises use of an adsorption indicator, and which involves the use of an organic acid (a) with the requisite acidity, and (b) is in powder form prior to use. Such an acid must not interfere with the titrimetric method based on silver, and must also not interfere with the method used by the operator to correct for the presence of thiocyanate ion, which often is present in widely used, non-chromogenic developer formulations employed for the development of color reversal methods.
This invention satisfies the above object. Thus, this invention comprises provision of methods, which employ citric acid, or other suitable organic acid, as an acidifying agent.